A Brazilian nurse who recovered from Covid-19 but got reinfected with the nation's new variant has sparked major concerns the mutation could hamper the hope of immunity.
The variant has spooked UK officials into banning all flights from Brazil, with experts warning the mutation may be able to get past immunity developed from older versions of Covid-19.
The 45-year-old nurse became ill with the new variant in October, 5 months after she had recovered from an older Covid-19 strain.
Officials say her symptoms were worse the second time.
Researchers from the Oswaldo Cruz Foundation, a science institute in Rio de Janeiro, warned that mutations on the new variant could increase the risk of reinfection.
They wrote that "viral evolutions may favour reinfections", claiming recently spotted variants "have raised concern on their potential impact in infectivity and immune escape".
Amid growing fears about the Brazilian variant, the UK Government today banned all travellers from Portugal, South America, Panama and Cape Verde in a bid to stop it from wreaking havoc in Britain.
The UK's chief scientific adviser, Sir Patrick Vallance, admitted that "we don't know for sure" how the new variant will affect vaccines and immunity.
However, despite fears of reinfection, Vallance told ITV's Peston show there was no evidence any of the variants led to more severe disease or could get around the immune system.
He said: "There's no evidence at all with any of these variants that it makes the disease itself more severe.
"So the changes that we're seeing with the variants are largely around increased transmission.
"[There's] no evidence yet for the UK version that it makes a difference in terms of how the immune system recognises it, and if you've been exposed to the old variant or you've had a vaccine, it looks like that's going to work just as well with this new variant for the UK one.
"The South African one and Brazilian one, we don't know for sure. There's a bit more of a risk that this might make a change to the way the immune system recognises it but we don't know. Those experiments are under way."
The news comes after the New Zealand Government announced all travellers from the UK would have to test negative for Covid-19 before returning to New Zealand.
The new UK variant of the Covid-19 virus has reached New Zealand shores but remains contained in managed isolation.
However, experts say an outbreak of the new variant would mean further lockdowns.
A level 4 lockdown longer than that back in March would be needed to stamp out new strains of Covid-19 which had potential for "explosive exponential growth" if they entered the community, scientists say.
On Monday it was revealed there were already 19 cases of the United Kingdom strain detected in New Zealand since December 13 and one case of the South African variant.
Professor Michael Plank, of Te Pūnaha Matatini and University of Canterbury, said the new variant called B.1.1.7, which has exploded across the UK, and the similar variant found in South Africa, had "potential for explosive exponential growth".
"There is no evidence that either of these new variants causes more severe disease than the original.
"But, there is strong evidence that the B.1.1.7 variant spreads more easily from one person to another.
"This means that the number of new cases per infected person [the so-called R number] is 40-70 per cent higher than the original strain.
"This is a serious concern because of the potential for explosive exponential growth."